In a laser radar system, the radar beam is swept across a field by a number of means, such as a pair of rotating optical wedges, a rotating mirror or an acousto-optical modulator, which receives a variable signal to modulate the frequency of the laser beam to produce a sweeping action that depends on the frequency of the modulator compared to the output beam. Any of these systems may be used in a scanning mode in which return signals are correlated with the nominal angle at which the beam was directed when the return signal was received; or they may be used in a tracking mode in which a previously acquired target is followed by controlling the beam steering device in order to maintain the target return signal on a detector. As a particular example, the return signal from a target may strike a quadrant optical detector and the signals from that detector may be used to control the beam steering device in order to maintain the return signal centered on the detector.
A specialized application of a laser is used in a beam rider missile guidance system, in which a broad laser beam is directed at a target and the beam is spatially encoded so that a missile within the beam can receive and decode the laser beam to determine its position relative to the center of the beam. In such systems, the laser beam does not return to the origin so that it is not a radar system but rather a transmitting system. U.S. Pat. Nos. 4,245,800 and 4,215,324 illustrate different forms of such a system in which a fixed laser beam is spatially coded for the purpose of giving position information to a missile which is within the laser beam.
U.S. Pat. No. 4,227,261 discloses a system in which a pair of laser beams are swept mechanically by means of a rotating wedge system to impinge upon one among a number of bodies within the space swept out by the beams. The system locates the body within a defined space, directs a laser beam toward the body and transmits information to it. The system locates the bodies within the space by means of radiation reflected back to the origin.